The addition of resinous additives to polypropylene has been suggested for several different reasons, including the enhancement of heat-sealing properties.
U.S. Pat. No. 3,666,836 describes the use of hydrogenated polymers or copolymers of styrene to prepare heat-sealable polypropylene films.
U.S. Pat. No. 3,755,502 describes the use of a dipentene-isobutene copolymer in heat-sealable polypropylene composition.
U.S. Pat. No. 3,663,488 describes the use of a polyterpene, hydrogenated polyterpene, or a rosin derivative to provide polypropylene films suitable for twist wrapping.
U.S. Pat. No. 4,032,493 describes enhancing the printability of heat sealable blends of stereoregular polypropylene and a hydrogenated hydrocarbon polymer by the addition of a hydrocarbon wax which can be a Fischer-Tropsch process synthetic wax. Heat aging to improve printability is described.
U.S. Pat. No. 3,361,849 describes a heat sealable blend of polypropylene and a hydrogenated terpene hydrocarbon polymer.
U.S. Pat. No. 3,278,646 describes heat-sealable polypropylene film containing a terpene polymer.
U.S. Pat. No. 3,536,644 describes the use of low molecular weight polyethylene waxes in polypropylene blends to impart heat-sealability, and also discloses that, in that combination, the addition of slip additives also enhances heat-sealing characteristics.